The present invention relates to a fuel injection internal combustion engine, and more particularly to apparatus for sensing fuel injection quantity as a parameter indicative of the load on an engine of this kind.
It is well known that it is necessary to know engine speed and fuel injection quantity in order to know the load on an engine of this kind. A conventional fuel injection quantity sensing apparatus described in SAE 800167 includes a non-contact displacement meter or a piezoelectric element which senses the displacement or lift of a needle valve of the fuel injector fixed in the combustion chamber of the engine to supply its output to a waveform processing unit. This waveform processing unit outputs a pulse signal, the pulse width of which indicates the duration during which the needle valve is in the lifted position. The pulse signal and clock pulses from a clock pulse generator are supplied to a counter to count clock pulses while the pulse signal is at high level to determine a fuel injection duration. This determined fuel injection duration and engine speed are supplied to a calculating unit to calculate fuel quantity per injection in accordance with a desired relationship among engine speed, fuel injection period and quantity.
With this apparatus, when contaminants in the fuel are deposited on the needle valve and the nozzle and block the nozzle, the relationship between fuel injection duration and quantity may deviate greatly from the desired relationship and errors in the detection of fuel injection quantity increase.
Another conventional approach is to calculate a fuel injection quantity from the position of a control lever of a fuel injection pump. This method has the advantage of being almost unaffected by the blocking of the nozzle. However, since fuel injection quantities in different engines differ from one another due to the combined errors involved in the manufacturing and assembling of the corresponding governors and in the adjustment thereof, this technique will not achieve the desired detection accuracy of fuel injection quantity without checking for the respective relationships between the positions of the lever and the actual fuel injection quantity.
The present invention intends to eliminate the above drawbacks of the conventional detecting apparatus.